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International audience; Low-temperature superconductors are widely used in high-field magnets, mostly within Rutherford-type cables. The run for higher fields leads to greater forces on the conductor, which is pushed closer to its mechanical limit. Managing the higher strain and stress levels on the conductor supposes to perform simulation at the strand level, especially with strain-sensitive superconductors such as Nb3Sn. Three-dimensional models are necessary because inside of a magnet, the conductor is subject to a complex combination of axial and transverse loads. Superconducting cables are anisotropic composite structures that can comprise superconducting strands, insulation materials, stabilizing parts, porosities, etc. They have a multiscale architecture, the performance at the magnet scale being driven by the filament scale. This paper proposes a numerical approach for 3-D finite-element (FE) modeling of Rutherford cables, at the scale of the strand. The 3-D mesh of two reference cables is built with a simplified cable forming model. The accuracy of this geometrical model is assessed by comparing sections of the simulated mesh with tomographic data, using relevant criteria and specific geometry analysis tools. In this approach, the strand is considered as bimetallic, with a copper core, a superconducting bundle ring, and an outer copper ring. After mechanical 3-D FE computation on this bimetallic mesh, the strain/stress state on the local compounds of the strand (including Nb3Sn filaments) is obtained by strain projection. The strain/stress state on the Nb3Sn filaments can be used to estimate the cable current transport capability, thanks to the existing scaling laws.

The evolution of the three-dimensional (3D) morphology of a Si-based electrode upon cycling (1st discharge, 1st charge and 2nd discharge) is studied by in-situ synchrotron X-ray tomography. The Si-based electrode is constituted of silicon/carbon black/carboxymethylcellulose (Si/CB/CMC) embedded in a commercial carbon fiber paper, acting as a flexible 3D current collector. Its initial areal discharge capacity is 4.9 mAh cm −2 . A reconstructed volume of 293 × 293 × 137 μm 3 is analyzed with a resolution of ∼0.3 μm. Three phases are identified: (i) the solid phase (C fibers + Si + CB + CMC), (ii) the electrolyte phase (pores filled with electrolyte) and (iii) the gas phase (electrolyte-free pores). Their respective volume fraction, size distribution and connectivity, and also the dimensional changes of the electrode along the three axes are quantified during cycling. At the beginning of the 1st discharge (lithiation), the formation of gas channels attributed to the reductive electrolyte decomposition is observed. During the 1st charge, large cracks are formed through the electrode, which reclose during the subsequent discharge. The electrode expansion/contraction due to the Si volume change is partially irreversible, occurs mainly in the transverse direction and is much larger in the bottom part of the electrode.

The ductility of Al alloys is dictated by the nucleation, growth and coalescence of small internal voids originating from intermetallic particle fracture and from the presence of pre-existing porosity. The ductility is degraded when intermetallic particles are large and clustered. A low ductility adversely impacts both forming operations and the integrity of structural components. Local stirring using a friction stir processing (FSP) tool is shown here to very significantly increase the fracture strain of the Al alloy 6056 sometimes by more than a factor of two while making it more isotropic. Three reasons for the ductilization are unravelled based on 3D microtomography: (i) FSP breaks the large intermetallic particles into smaller, and thus stronger, fragments, (ii) FSP closes the pre-existing porosity; (iii) FSP randomizes the particle distribution. Hence, FSP positively impacts three of the main causes of ductility loss in metallic alloys. From an applicability viewpoint, this method has the potential to locally improve ductility of sheets at locations where forming involves large strains or of structural components at stress concentration points.

Lattice structures of 100Cr6 steel were manufactured from metallic-based inks by robotic-assisted deposition (robocasting) using Pluronic F-127 solution. The stability and pseudo-plastic behavior of the ink were optimized, and allowed printing through 200–840 μm nozzles, leading to macroporous architectures composed of 300–600 μm diameter rods separated by 90–350 μm pores, after debinding and sintering. A second level of porosity (sub-micron size) was controlled by adjusting the sintering temperature. The linear shrinkage due to drying and thermal consolidation was evaluated from images obtained by micro-tomography and volumes measured by mercury intrusion porosimetry. Whatever the thermal treatments, the microstructure was always mainly composed of ferrite – α. The mechanical properties were estimated both at a local level (Young modulus and hardness of the rods by nanoindentation, coherent with those of 100Cr6 steel) and at the architecture level (stress-strain curve of the structures, showing a plastic behavior related to a good consolidation of the structure). Thus, dense metallic lattice structures with a regular macroporosity and interesting mechanical properties can be easily obtained with these water-based metallic inks, which do not require a complex formulation nor high organic content as reported in literature. Keywords: Additive manufacturing, Robocasting, Mercury intrusion porosimetry, X-ray micro-tomography, Microstructural characterization, Mechanical properties

EBM as-built fatigue samples were manufactured from both fresh and recycled powder. They were characterised by laboratory X-ray tomography in order to observe the porosity and surface state. Chemical etching was used and a clear improvement of the surface geometry was observed and quantified through a roughness reduction. Fatigue tests were performed on as-built and etched samples. The fatigue resistance obtained for as-built samples is lower than that of machined samples; powder recycling tends to also diminish the fatigue resistance whereas chemical etching improves it significantly. The study of the fracture surfaces coupled with the comparison of tomographic scans before and after failure shows that the crack leading to failure always initiate from a surface notch-like defect resulting from a lack of fusion.

cited By 0; Ideal dielectric materials for microelectronic devices should have high directionally tailored thermoconductivity with low dielectric constant and loss. Hexagonal boron nitride (hBN) with excellent thermal and dielectric properties shows a promise for the fabrication of thermoconductive dielectric polymer composites. Herein, a simple method for the fabrication of lightweight polymer/hBN composites with high directionally tailored thermoconductivity and excellent dielectric properties is presented. The solid polymer/hBN composites are manufactured by melt-compounding and injection molding. The porous composites are successfully manufactured in an injection molding process through supercritical fluid (SCF) foaming. X-ray tomography provides direct visualization of the internal microstructure and hBN orientation, leading to an in-depth understanding of the directionally dependent thermoconductivity of the polymer/hBN composite. Shear-induced orientation of hBN platelets in the solid HDPE/hBN composites leads to a significant anisotropic thermal conductivity. The solid HDPE/23.2 vol % hBN composites show an in-plane thermoconductivity as high as 10.1 W m-1 K-1, whereas the through-plane thermoconductivity is limited to 0.28 W m-1 K-1. However, the generation of a porous structure via SCF foaming imparts in situ exfoliation, random orientation, and interconnectivity of hBN platelets within the polymer matrix. This results in highly isotropic thermoconductivity with higher bulk thermal conductivity in the lightweight porous composites as compared to their solid counterparts. Furthermore, the electrically insulating composites developed in this study exhibit low dielectric constant and ultralow dielectric loss. Thus, this study presents a simple fabrication method to develop lightweight dielectric materials with tailored thermal conductivity for modern electronics. © 2019 American Chemical Society.

A detailed identification, using X-ray microtomography, of the filament trajectories within twisted single and multi-ply continuous filament yarns is presented in this article, to accurately determ...

International audience; Damage evolution in ductile metals is characterized by the nucleation, growth and coalescence of small internal voids. Many laws and studies have been developed to understand and predict damage. Numerical modeling, based on full field microstructure acquisition have proven also to be quite efficient. Real microstructure input are of utmost importance as some studies have shown that the deviation from the average behavior for voids growth can be huge and therefore allows a single cavity to drive the damage behavior and lead to failure. We develop the dedicated tool to analyze individually voids during in situ test and use results as input for numerical simulations.

International audience; In this work, capillary structures are manufactured by sintering of copper and zirconia powders using different sintering parameters, in order to obtain porous samples with various hydrodynamic characteristics and surface properties. A specific test bench is designed to reproduce a capillary evaporator of a LHP decoupled from the remaining of the loop and enables the determination of the evaporator heat transfer coefficient and optimum heat flux at the occurrence of the operating limit. The influence of the surface properties on the evaporator thermal behaviour is investigated by polishing the copper wick surface in contact with the evaporator fins, or by coating the zirconia wick with a thin gold layer. It is shown that polishing decreases the thermal performance when the size of the gap between the evaporator fins and the wick becomes lower than the pore size. The coating enables to enhance the evaporator thermal performance, probably by a reduction of the thermal contact resistance or by a favourable surface wettability effect, reducing the strong effect of the wick topography on the optimum heat flux value. Finally, a data mining approach is proposed which highlights the preponderant effect of the surface quality on the evaporator heat transfer coefficient.

Mg-Ca(-Zn) alloys were subjected to hot compression at temperatures ranging from 350 ∘C to 450 ∘C and strain rates of 10−3 to 10 s−1. In the corresponding flow curves, the peak stress appeared at very low strain rates (less than 0.05) followed by steady state at a constant stress, indicating the occurrence of dynamic flow softening, which is a typical signature of dynamic recrystallization (DRX). The DRX was greatly affected by the deformation conditions and Ca/Zn contents, and optical and scanning electron microscopy analysis revealed that the DRX induced rearrangement of the complex dendritic microstructure during compression. Optimal parameters for the deformation were identified. These indicate deformation conditions where the processing is safe and easy. This in turn is likely to enable widening of the range of applications of Mg-Ca(-Zn) alloys.

Aortic dissection represents a serious cardio-vascular disease and life-threatening event. Dissection is a sudden delamination event of the wall, possibly leading to rupture within a few hours. Current knowledge and practical criteria to understand and predict this phenomenon lack reliable models and experimental observations of rupture at the lamellar scale. In an attempt to quantify rupture-related parameters, the present study proposes an analytical model that reproduces a uniaxial test on medial arterial samples observed under X-ray tomography. This model is composed of several layers that represent the media of the aortic wall, each having proper elastic and damage properties. Finite element models were created to validate the analytical model using user-defined parameters. Once the model was validated, an inverse analysis was used to fit the model parameters to experimental curves of uniaxial tests from a published study. Because this analytical model did not consider delamination strength between layers, a finite element model that included this phenomenon was also developed to investigate the influence of the delamination on the stress-strain curve through a sensitivity analysis. It was shown that shear delamination strength between layers, i.e. mode II separation, is essential in the rupture process observed experimentally.

International audience; The thermo-mechanical properties of a ferritic-steel-based metal matrix composite reinforced with titanium diboride (TiB 2) particles were studied using synchrotron X-ray diffraction. The samples were subjected to in situ heat treatment to investigate the effect of the mismatch in the coefficient of thermal expansion between the matrix and reinforcement. In addition, in situ tensile tests were performed to examine the load partitioning in the composite. Load transfer from the ferritic matrix to the TiB 2 particles was observed at the onset of plasticity in the matrix.

Liquids metal dealloying is a new technology to create porous materials. In this study, a commercial Incoloy 825 nickel superalloy is dealloyed for 1 h at 3 different temperatures to elaborate a fully porous FeCr-based metal with 3 different porous microstructures. The resulting porous metals showed unimodal pore distribution, hierarchical structure or, contain large ligaments inclusions. The passivation ability of the porous material was conformed irrespective of the microstructure. This letter proves the possibility of fabricating low cost high specific surface materials for electrochemical applications.

Hydrogen energy is a possible solution for storage in the future. The resistance of packaging materials such as stainless steels has to be guaranteed for a possible use of these materials as containers for highly pressurized hydrogen. The effect of hydrogen charging on the nucleation and growth of microdamage in two different austenitic stainless steels AISI316 and AISI316L was studied using in situ tensile tests in synchrotron X-ray tomography. Information about damage nucleation, void growth and void shape were obtained. AISI316 was found to be more sensitive to hydrogen compared to AISI316L in terms of ductility loss. It was measured that void nucleation and growth are not affected by hydrogen charging. The effect of hydrogen was however found to change the morphology of nucleated voids from spherical cavities to micro-cracks being oriented perpendicular to the tensile axis.

cited By 1; International audience; In situ tensile tests were carried out on notch axisymmetric samples of as-cast (α+β) Ti alloy to analyze evolution of void/micro-crack with the help of X-ray Synchrotron tomography. The results indicate that junctions or boundaries of α colonies could be the most vulnerable sites for voids nucleation. In addition, during the growth and coalescence procedure, “ligaments” could be observed on the voids/micro-crack. A “bypassing & fracture” propagating approach was proposed and validated to interpret the existence of “ligaments”. In the propagating procedure, due to lacking of hard precipitations, microstructure zone and other inserting colony could play a role as hard obstacle in the growing path. This could induce a “bypassing & fracture” propagating approach for void coalescence and micro-crack growth. © 2019 Elsevier B.V.

International audience; The dynamic gas injection method with high-speed horizontal oscillation could reduce the cell size and improve the cell quality of aluminum foams, so it is of interest to study the compressive performance and deformation mechanism of the foams produced with this process. In-situ compression in X-ray tomography was used for this research. Results have shown that the plateau stresses of bulk aluminum foams prepared by the dynamic gas injection method are in the range of 0.3 ~ 11 MPa. When the cell size is reduced to around 1 mm, the plateau stress could reach 22 MPa. In addition, the brittle deformation characteristics of aluminum foams in the quasi-static compression process are obvious. The dynamic gas injection method could greatly improve the mechanical properties of aluminum foams, and aluminum foams prepared by this method have a better compressive performance compared to that prepared by static method even at the same relative density. The uniformity of the cell size and sphericity also affects the mechanical properties. The result of in-situ compression shows that there are two main failure modes for cell walls of aluminum foams: the fracture after buckles of the cell walls and the direct fracture of the cell walls. The aluminum foams prepared by the dynamic gas injection method could have a wide application prospect due to its superior compressive performance.

International audience; Hardystonite scaffolds produced by ceramization of 3-D printed preceramic filled polymer were impregnated with chitosan solutions, later neutralized into physical hydrogels. Hardystonite bioceramic and chitosan physical hydrogel were chosen for their interesting biological properties as potential bone substitutes. Five impregnation protocols, differing in impregnation vacuum, chitosan concentration, chitosan to hardystonite mass ratio and base used for chitosan gelation were studied. The composition, micropore structure and surface morphology of impregnated scaffolds were determined. Impregnated hardystonite scaffolds were tested to find out the effect of impregnation protocols on elastic and dissipative mechanical properties of the composites. The capacity for energy dissipation and for load bearing increased as chitosan content increased in the composites. Thus, 3-D architectured biocomposites with enhanced mechanical properties can be manufactured following the method shown in this article.

International audience; The actual displacement field in a glass during an in-situ Vickers indentation experiment was determined by means of X-ray tomography, thanks to the addition of 4 vol % of X-ray absorbing particles, which acted as a speckle to further proceed through digital volume correlation. This displacement was found to agree well with the occurrence of densification beneath the contact area. The intensity of the densification contribution (Blister field proposed by Yoffe) was characterized and provides evidence for the significant contribution of densification to the mechanical fields. Densification accounts for 27% of the volume of the imprint for the studied glass, that is expected to be less sensitive to densification than amorphous silica or window glass. A major consequence is that indentation cracking methods for the evaluation of the fracture toughness, when they are based on volume conservation, as in the case of Hill-Eshelby plastic inclusion theory, are not suitable to glass. The onset for the formation of the subsurface lateral crack was also detected. The corresponding stress is z 14 GPa and is in agreement with the intrinsic glass strength.

Aluminium alloys are commonly used in studies related to Friction Stir Welding (FSW) and Processing (FSP), due to their wide variety of applications. FSP provides grain size reduction; intermetallic rounding, size reduction and redistribution; and an overall increase in ductility. Moreover, FSP becomes a popular method for Metal Matrix Composites (MMCs) production, owing to the homogeneous distribution of reinforcement particles and their good interface with the initial matrix. In this work, a healable Al alloy from a base of Al 6063 is produced using FSP. FSP causes a uniform healing particle precipitation (with a size up to 1 μm), as well as the breakage of Fe-rich intermetallics in the nugget zone. This changes damage mechanism, meaning the classical failure source of Al 6063 - Fe-rich intermetallics - remain intact while the healing particles are broken. Further, at the healing stage, a heat treatment is applied to heal the damage.

A ferritic steel composite with titanium diboride (TiB2) particles produced by in-situ precipitation was studied by means of synchrotron X-ray diffraction. Samples were subjected to an in-situ heat treatment which allowed to study the mismatch in the coefficient of thermal expansion between the matrix and the reinforcement. In addition, in-situ tensile tests enable the observation of the load partitioning in the composite. A transfer of load from the ferritic matrix to the TiB2 particles was seen at the beginning of the plastic regimen of the matrix.

Thin Ti-6-Al-4V tensile fatigue specimens were specifically designed to mimic struts of a lattice structure. Those samples were submitted to HIP and chemical etching that are thought suitable for complex geometries (machining was excluded). The effect of each post-treatment, as well as their combination on the fatigue performance is evaluated and quantified. Fatigue cracks are found to systematically initiate from surface defects. An original approach based on a full-3D non-destructive characterization by X-ray microtomography is developed to identify the population of those defects and rank them based on their size. Kitagawa-Takahashi diagrams are then used as a predictive tool regarding fatigue failure of samples containing defects. We show that ranking the defect size alone does not fully reflect the harmfulness of the identified defects.

International audience; As-built Ti-6Al-4V thin parts were manufactured in three different orientations using EBM and characterized by laboratory X-ray tomography. Fatigue tests were performed. The comparison with results for machined samples from the literature showed a large reduction of fatigue strength. SEM observations of the fracture surfaces showed that surface defects which were identified as notch-like defects on tomographic images caused the failure. Their impact on fatigue results was rationalized by Kitagawa-Takahashi diagrams. A build orientation impact on the fatigue properties was observed and linked to its effect on defects distributions and crack growth. The limits of roughness measurements were also discussed.

cited By 0; International audience; Damage evolution during tensile straining of an AlSi12Ni alloy has been analyzed in situ at synchrotron source using microtomography and in the scanning electron microscope by surface imaging. It is shown that damage development in the analyzed alloy presenting an interconnected network of intermetallic phases is completely different from damage progression previously observed in materials with disperse distribution of particles. In the present material, which is typical for most eutectic structures, damage is dominated by the rupture of the brittle intermetallic phase while void growth is limited by a shielding effect of the intermetallic particles encasing the void. Primary voids exhibit a size close to the thickness of branches of the intermetallic phase. Final failure occurs by void coalescence, but without the formation of secondary voids. Damage analysis from tomographic scans was only possible by applying 3D image correlation to successive reconstructions, which thanks to its sub-voxel resolution, could satisfactorily detect the volume fraction of small-voids inaccessible by conventional thresholding. The presence of many small voids issued from the breakage of the intermetallic phase also was confirmed by scanning electron microscopy imaging performed at higher resolution. © 2019 Acta Materialia Inc.

International audience; Bone substitute fabrication is of interest to meet the worldwide incidence of bone disorders. Physical chitosan hydrogels with intertwined apatite particles were chosen to meet the bio-physical and mechanical properties required by a potential bone substitute. A set up for 3-D printing by robocasting was found adequate to fabricate scaffolds. Inks consisted of suspensions of calcium phosphate particles in chitosan acidic aqueous solution. The inks are shear-thinning and consist of a suspension of dispersed platelet aggregates of dicalcium phosphate dihydrate in a continuous chitosan phase. The rheological properties of the inks were studied, including their shear-thinning characteristics and yield stress. Scaffolds were printed in basic water/ethanol baths to induce transformation of chitosan-calcium phosphates suspension into physical hydrogel of chitosan mineralized with apatite. Scaffolds consisted of a chitosan polymeric matrix intertwined with poorly crystalline apatite particles. Results indicate that ink rheological properties could be tuned by controlling ink composition: in particular, more printable inks are obtained with higher chitosan concentration (0.19 mol·L−1).

cited By 0; International audience; The use of light components possessing tailored functional properties will represent one of the main issues for the development of new products. Open cells foams, where porosity is engineered in order to grant for lightness, high geometrical surface, interconnectivity and permeability, can be shaped using various techniques and possess regular or irregular structure. In this work, Ti6Al4V foams were produced using the gelcasting route, a technique usually employed for ceramics. Numerical simulations were carried out directly on 3D images of the foam's microstructure obtained by X-ray 3D µCT in order to predict the gas permeability properties of the produced samples. The obtained results were compared to experimental measurements of gas permeability. This approach could be useful for the prediction of Newtonian fluids permeability behavior of non-periodic and complex porous structures. © 2018 Elsevier B.V.

An integrated experimental-numerical method combining a realistic microstructure-based isotropic crystal-plasticity (CP) model and fracture surface analysis was adapted to analyze the fracture behavior of the titanium alloy Ti-6Al-4V. A hybrid fracture mode consisting of cleavage facets and elongated dimples was observed and analyzed. With the help of numerical simulations and post-mortem SEM, the micro-mechanism of the hybrid fracture mode was revealed. The results show that ruptured α lamellae can be linked to cleavage facets induced by the development of voids. Simultaneously, hard β lath can function as walls that separate two neighboring arrays of voids or micro-cracks within the α lamellae. The origin of this behavior can be associated with a heterogeneous stress/strain distribution in the α/β phases, which was revealed via numerical simulations. Further, the influence of the α grain orientation on the void evolution was investigated by varying the Schmid factor of the grains in simulations.

Microheterogeneous materials such as metal foams exhibit a strong structure-property-relationship. The macroscopic material properties depend on the pore geometry and especially on the strut geometry and the microstructure of the struts such as the grain structure. Since the grain structure in the struts differs from that of the corresponding bulk material, it is of utmost importance to perform microtensile tests on individual struts. Previous works on aluminium foams outlined strong scattering in this micromechanical properties. A possible reason for the scattering might be micro-porosity and inclusions in the struts resulting from the manufacturing of metal foams by investment casting. The present contribution deals with ex situ and In situ microtensile tests to elucidate reasons for the scattering in the micromechanical properties determined from microtensile tests on individual struts. In situ tensile tests using high resolution X-ray computed tomography were used to study the microstructural failure mechanisms in aluminium foam struts. The results were further proven by additional ex situ tensile experiments on struts, which were analysed by low resolution X-ray computed tomography prior to tensile testing to allow for more specimens and hence for better statistics. Micro-porosity and primary inclusions were found to be the main reason for differences in the micromechanical properties of individual aluminium foam struts.

International audience; Enameloid, the hyper-mineralized tissue covering shark teeth is a complex structure resulting from both ameloblast and odontoblast activity. The way these two types of cells interact to set up this tissue is not fully understood and results in the formation of subunits in the enameloid: the Single Crystallite Enameloid (SCE) and the Bundled Crystallite Enameloid (BCE). Using the Focused Ion Beam Nanotomography (FIB-nt), 3D images were produced to assess the relationship between the SCE and BCE of one fossil and one recent neoselachian shark teeth. 3D analysis of crystallite bundles reveals a strong connection between the crystallites forming the SCE and those forming the bundles of the Radial Bundle Enameloid (RBE), a component of the BCE, although it has been suggested that SCE and BCE have a different origin: epithelial for the SCE and mesenchymal for the BCE. Another significant result of the use of FIB-nt is the visualization of frequent branching among the radial bundles forming the RBE, including horizontal link between adjacent bundles. FIB-nt demonstrates therefore a strong potential to decipher the complex evolution of hyper-mineralised tissue in shark teeth, and, therefore, to better understand the evolution of tooth structure among basal Gnathostomes.

Summary Gypsum microstructural evolution at elevated temperatures has been characterized in situ by environmental scanning electron microscopy and high-temperature X-ray tomography. As temperature increases, the observed changes in gypsum crystal morphology are related to the consequences of water loss that leads to crystal reorganization in order to minimize the specific surface. The influence of environmental scanning electron microscopy experimental conditions on the mechanisms observed is also discussed. High-temperature X-ray tomography gives quantitative information on porosity evolution with thermal loading. The results obtained are successfully correlated with macroscopic shrinkage measurements performed during dilatometry tests. Copyright © 2016 John Wiley & Sons, Ltd.

We have developed flexible polymer-gel electrolytes based on a polyacrylate cross-linked matrix that confines an ionic liquid doped with a lithium salt. Free-standing solid electrolyte membrane is obtained after UV photo-polymerization of acrylic monomers dissolved inside the ionic liquid/lithium salt mixture. The liquid precursor of the photo-ionogel may also be directly deposited onto porous composite electrode, which results in all-solid state electrode/electrolyte stacking after UV illumination. Minor variations in the polymer component of the electrolyte formulation significantly affect the electrochemical behavior in LiFePO4/lithium and lithium/lithium cells. The rate performance increases with an increase of the ionic conductivity, which decreases with the polymer content and decreases with increasing oxygen content in the polyacrylate matrix. Their fairly low modulus endow them weak and beneficial pressure-sensitive-adhesive character. X-Rays Tomography shows that the solid-state photo-ionogel electrolytes keep their integrity upon cycling and that their surface remains smooth. The coulombic efficiency of LiFePO4/lithium cells increases with an increase of the adhesive strength of the photo-ionogel, suggesting a relationship between the contact intimacy at the lithium/photo-ionogel interface and the efficiency of the lithium striping/plating. In lithium/lithium cells, only the photo-ionogels with the higher adhesion strength are able to allow the reversible striping/plating of lithium.

The 3D morphology of LiNi1/3Mn1/3Co1/3O2 (NMC), LiFePO4 (LFP), and blended NMC/LFP electrodes envisioned for electric vehicles Li–ion batteries is characterized by both synchrotron X-ray tomography and FIB/SEM tomography. The size distribution of the active materials, the carbon phase and the pores, the specific surface area of the different solid phases, the concentration variations of the various phases through the total electrode thickness (X-ray tomography) or in smaller volumes (FIB/SEM tomography) are quantified. Results are assessed in relationship with the electrode composition and with their typical slurry rheological properties. Several heterogeneities are evidenced as the fingerprint of phenomena associated with the different processing steps of the electrodes.

International audience; To design lightweight plasterboard and optimize the compromise between thermal resistance and mechanical strength, it is important to characterize its strength as characterized with the normative Nail pull test. Understanding the phenomenology of this test is the key to identifying the limiting factor in terms of load carrying capacity. In this work, the degradation mechanisms of lightweight plasterboard are analyzed via tests conducted in-situ in a laboratory tomograph. Through the analysis of the kinematics by digital volume correlation, the dierent mechanisms at play up to failure mechanism have been identied, i.e., quasi-elastic regime, failure of the roller coating layer, core compaction and core failure. The compaction of the core by the collapse of porosity in compression is recognized as the limiting factor in terms of compressive strength and tearing resistance.

International audience; The work focuses on the structural and mechanical characterization of Co-Cr-Mo cellular samples with cubic pore structure made by Electron Beam Melting (EBM). X-ray tomography was used to characterize the architecture of the sample. High resolution images were also obtained thanks to local tomography in which the specimen is placed close to the X-ray source. These images enabled to observe some defects due to the fabrication process: small pores in the solid phase, partially melted particles attached to the surface. Then, in situ compression tests were performed in the tomograph. The images of the deformed sample show a progressive buckling of the vertical struts leading to final fracture. The deformation initiated where the defects were present in the strut i.e. in regions with reduced local thickness. The finite element modelling confirmed the high stress concentrations of these weak points leading to the fracture of the sample.

International audience; This paper describes an in-situ tensile test in synchrotron tomography achieved for the first time with a frequency of 20 tomograms per second (20 Hz acquisition frequency). This allows us to capture rapid material fracture processes, such as that of a metal matrix composite composed of 45 % of alumina particles embedded into 55 % of pure aluminium, which fractures by the sudden coalescence of internal damage. Qualitatively, the images show the nucleation and propagation of a crack during 9 s leading to total fracture of the sample. The images are then post-processed quantitatively to analyze the evolving shape of the crack and to derive the instantaneous speed of its tip. It is shown that the crack clearly propagates from one particle to the next, pausing briefly before propagating to the next particle, lending experimental support to a local load sharing analysis of the fracture of this class of composite.

International audience; Ductile failure of three 6xxx serie aluminium alloys has been characterized and modelled for about thirty hardening conditions each. These alloys involve relatively similar composition and volume fraction of second phase particles. The tensile mechanical properties show the expected decrease of fracture strain with increasing strength but also major differences among the different alloys with a factor ten in terms of reduction of area at fracture between best and worst case. The origin of these differences is unraveled by detailed characterization of the void nucleation, growth and coalescence process involving in situ 3D microtomography. A cellular automaton model, involving a high number of particles with distributions of position, sizes and void nucleation stress is developed to predict the fracture strain. Excellent predictions are obtained based on the same unique nucleation stress distribution versus particle size for the three alloys. The key element setting the fracture strain is the effect of particle size distribution and spatial distribution on the void nucleation and coalescence processes. The dependence of ductility on strength is properly captured as well.

Silicon is attractive as negative electrode material for Li-ion batteries (LIBs) to increase their energy density [1]. The main challenge is to deal with the large silicon volume expansion induced by its lithiation, which damages the mechanical integrity of the electrode, and produces an unstable solid electrolyte interphase (SEI). Recently, we have discovered a post-processing treatment, called maturation, which very significantly improves the mechanical and electrochemical stabilities of silicon-based electrodes made with polycarboxylic acid binders [2-4]. It consists of storing the electrode in a humid atmosphere for a few days before drying and cell assembly. We found that during maturation, the atmospheric-induced corrosion of the current collector releases oxidized copper species that migrate into the electrode to physically crosslink the binder phase, substantially modifying its resiliency to the silicon volume variation as shown by various in situ and operando characterizations. The pre-addition of a small amount of copper or zinc salt in the electrode slurry allows to reach similar improvement of electrochemical performance than maturation [5]. This reveals that there is great potential to explore coordination chemistry to design new, more efficient binders through the medium strength and dynamic nature of coordination bonds [6]. Acknowledgments The authors thank the Natural Sciences and Engineering Research Council of Canada (NSERC) (grant RGPIN-2016-04524) and Transition Énergétique Québec (TEQ) (grant Techno-0040-0001) for financial support of this work. References [1] M.N. Obrovac, Si-alloy negative electrodes for Li-ion batteries. Current Opinion in Electrochemistr, 2018, 9, 8–17. [2] Z. Karkar et al., How silicon electrodes can be calendered without altering their mechanical strength and cycle life J. Power Sources, 2017, 371, 136-147. [3] C. Real Hernandez et al., A Facile and Very Effective Method to Enhance the Mechanical Strength and the Cyclability of Si-Based Electrodes for Li-Ion Batteries, Adv. Energy Mater, 2017, 1701787. [4] V. Vanpenne et al., Adv. Energy Mater, Dynamics of the morphological degradation of Si-based anodes for Li-ion batteries characterized by in-situ synchrotron X-ray tomography, Adv. Energy Mater. 9, 2019, 1803947 [5] D. Mazouzi et al., CMC-citric acid Cu(II) cross-linked binder approach to improve the electrochemical performance of Si-based electrodes Electrochimica Acta, 2019, 304, 495-504. [6] T. Devic, B. Lestriez, L. Roué, Silicon Electrodes for Li-Ion Batteries. Addressing the Challenges through Coordination Chemistry, ACS Energy Letters, ACS Energy Lett., 2019, 4, 550−557.

Lithium (Li) metal is the most promising anode battery material to be implemented in stationary and electric vehicle applications [1]. For years, its use and subsequent industrialization was hampered because of the inhomogeneous Li electrodeposits onto Li metal leading to dendrite growth [2]. The use of solid polymer electrolyte is a solution to mitigate dendrite growth but the Li redox processes, stripping and plating, remain heterogeneous. Blue Solutions compagny is already commercializing lithium metal batteries using a solid polymer electrolyte to prevent dendrite growth. A precise characterization of the behaviour of these heterogeneities during cycling is essential to move towards an optimized anode. During our research, we have developed a characterization method based on X-ray tomography applied to model Li symmetric cells to quantify and spatially probe the Li stripping/plating process. Ante- and post-mortem cells are recut in order to allow a 1µm voxel size in a conventional laboratory scanner. The reconstructed cell volume is post-processed to numerically re-flatten the Li electrodes, allowing us a subsequent precise measurement of the electrode and electrolyte thicknesses and revealing local interface modifications. This in-depth analysis brings information on the location of heterogeneities and the impact on the electrode microstructure both at the electrode grains and grain boundaries. This simple methodology permits to finely retrieve and then surface-map the local current density at both electrodes based on the local thickness change during the redox process (see Figure 1a : 2D map of the cathode local current density variations overlaped with grain boundaries pattern (image analysis of a cell after moving 22µm of lithium)). Thanks to quantitative data that can be extracted from the 2D maps (see Figure 1b: anode and cathode quantitative distribution of local current density variations), we show that the plating process (reduction) induces more pronounced heterogeneous deposits compared to the stripping (oxidation) one. The existence of cross-talking between the electrodes is also highlighted. [1] Wu Xu et al., Energy Environ. Sci. 7, no 2 (2014): 513-37 [2] Xin-Bing Cheng et al., Chemical Reviews 117, n°15 (2017): 10403-73 Figure 1

International audience

Visualization and quantification of the morphological changes of Si-based electrodes occurring upon cycling are essential for better understanding their degradation mechanism and for optimizing their formulation. In this context, in-situ and ex-situ X-ray computed tomography (XRCT) analyses are here performed on Si-based electrodes for different cycling steps and at different scales (i.e. from the composite electrode level down to the Si particle one). Three different cell configurations and four different X-ray sources (one laboratory and three synchrotrons) have been used and their impact on the image resolution/quality and the segmentation of the different solid, electrolyte and gas phases of the composite electrodes is highlighted. From these complementary XRCT analyses with a voxel size ranging from 0.8 to 0.05 μm, key morphological features have been studied such as (i) the volume expansion/contraction of the electrode, (ii) the dynamics of the electrode macrocracking, (iii) the initial solid electrolyte interphase (SEI) layer growth and related formation of gas and consumption of electrolyte, which strongly depend on the presence of fluoroethylene carbonate in the electrolyte, (iv) the evolution of the electrode porosity and macrocrack volume fraction/connectivity/width after prolonged cycling.

International audience; The microstructures of Li-ion positive composite electrodes designed for EVs have been characterised at different scales and in particular by FIB/SEM nanotomography. These electrodes are composed of Li(Ni 0.5 Mn 0.3 Co 0.2)O 2 , carbon black (CB), and polyvinylidene fluoride (PVdF). The component proportions in the electrodes and the electrode densities were varied. Specific image analysis tools have been developed to quantify the microstructure parameters that will influence the transport and exchange properties of ionic and electronic charges during battery operation. Different porosities have been highlighted, in particular the micrometric porosity which appears to be the most effective for the ion diffusion in the liquid electrolyte due to its low tortuosity and large intra-connectiviy. Different parallel paths for the transport of electrons in solid phases such as the CB/PVdF percolating network and a hybrid one consisting of CB/PVdF islands distributed on the NMC cluster surface and the NMC grains pertaining to these clusters. This last network can be effective when the CB/PVdF islands allow the electrons to short-circuit the resistive NMC grain boundaries.

A detailed understanding of heat transfer and flow is critically important for the pyrolysis of carbonaceous feedstock in fixed bed reactors. In this paper, multimode transport phenomena are simulated by direct pore level simulation on representative digitized samples to retrieve the heat-transfer and pressure-drop properties of highly porous fixed beds of oak-wood chips, which exhibit anisotropic solid-phase tortuosity. A comparison of the direct pore level simulation and simple models of porous media with simple morphologies shows that simple models cannot be used to determine the transport properties of a material with a complex morphology, such as fixed beds of wood chips. Because of drying and devolatilization, the effective thermal conductivity of wood chips decreases with increasing temperature. Heat conduction passes preferentially through the fluid because wood chips have very low thermal conductivity. This study also shows that the shrinking and cracking phenomena resulting from pyrolysis lead to a decrease in the porosity and solid-phase tortuosity and an increase in the specific area. At a high Reynolds number, the pyrolysis also diminishes the permeability but increases the inertial resistance to flow and the interfacial heat transfer.

The present work addresses the mechanisms of plasticity and damage nucleation in a Ti-6Al-4V alloy and its laser weld. To this end, in situ tensile tests are performed in a Scanning Electron Microscope (SEM) equipped with a Electron BackScatter Diffraction (EBSD) camera. The slip activity is automatically analyzed using a modified Schmid analysis. It is shown that the slip activity of the base metal consists mainly in prismatic, basal and pyramidal 〈a〉 slip. Damage nucleation in the vicinity of the β phase and at α grain boundaries is also evidenced in the base metal. In the α′ weld metal (a microstructure similar to the one often obtained in additive manufacturing Ti-alloy parts), plastic deformation results in a crystallographic rotation of the laths tending to align the 10 1 0 direction with the tensile axis. The rare events of crack initiation in the martensite are shown to occur along specific laths interfaces, former β grain boundary or twinned martensite needles.

International audience; In this study, finite element (FE) modeling of open-cell aluminum foams in tension was performed based on laboratory X-ray tomography scans of the materials at two different scales. High-resolution stitching tomography of the initial state allowed local intermetallic particles to be distinguished from internal defects in the solid phase of the foam. Lower-resolution scans were used to monitor the deformation and fracture in situ during loading. 3D image-based FE models of the foams were built to simulate the tensile behavior using a new microstructure-informed Gurson-Tvergaard-Needleman model. The new model allows quantitative consideration of the local presence of brittle intermetallic particles in the prediction of damage. It performs well in the discrimination of potential fracture zones in the foam, and can be easily adapted to any type of architectured material where both the global architecture and local microstructural details should be taken into account in the prediction of damage behavior.

International audience; X-ray tomography is used to produce three-dimensional images of an aluminium alloy foam with a high porosity (>93%). These data allow describing the foam structure from which a finite element model is derived to predict the thermal conductivity of the foam. The results are compared with experimental values measured by a new guarded hot plate apparatus adapted for the range of thermal conductivity values of interest. Good agreement is observed which validated the finite element model used to evaluate the thermal properties of any porous metallic foam with stochastic cell size and configuration. Furthermore, the thermal conductivity of the foam has also been predicted using previous analytical models. The differences with previous values show that it is important to account for the real geometry of the foam to get an accurate value of the thermal conductivity.

The freezing of colloidal suspensions is encountered in many natural and engineering processes. It can be harnessed through a process known as ice templating, to produce porous materials and composites exhibiting unique functional properties. The phenomenon by itself appears simple: a solidification interface propagates through a colloidal suspension. We are nevertheless still far from a complete understanding and control of the phenomenon. Such lack of control is reflected in the very large scattering of mechanical properties reported for ice-templated ceramics, largely due to the formation of structural defects. Through systematic in situ investigations, we demonstrate here the role of the suspension composition and the role of particle-particle electrostatic interactions on defect formation during ice templating. Flocculation can occur in the intercrystal space, leading to a destabilisation of the solid/liquid interface triggering the growth of crystals perpendicular to the main ice growth direction. This mechanism largely contributes to the formation of structural defects and explains, to a large extent, the scattering of compressive strength values reported in the literature., 19 pages, 9 figures

We investigate the ice-templating behaviour of alumina suspensions by in-situ X-rays radiography and tomography. We focus here on the formation and structure of the transitional zone, which takes place during the initials instants of freezing. For many applications, this part is undesirable since the resulting porosity is heterogeneous, in size, morphology and orientation. We investigate the influence of the composition of alumina suspensions on the formation of the transitional zone. Alumina particles are dispersed by three different dispersants, in various quantities, or by chlorhydric acid. We show that the height and the morphology of the transitional zone are determined by the growth of large dendritic ice-crystals growing in a supercooled state, and growing much faster than the cellular freezing front. When the freezing temperature decreases, the degree of supercooling increases. This results in a faster freezing front velocity and increases the dimensions of the transitional zone. It is therefore possible to adjust the dimensions of the transitional zone by changing the composition of alumina suspensions. The counter-ion Na+ has the most dramatic influence on the freezing temperature of suspensions, yielding a predominance of cellular ice crystals instead of the usual lamellar crystals., 15 pages, 9 figures